Current methods for applying polymer coatings on particle surfaces rely mainly on liquid-based techniques such as spray drying from polymer solutions. However, these methods suffer from particle agglomeration due to liquid bridges that form between the particles which then binds them together during solvent evaporation. Consequently, it is difficult to achieve coatings on individual particles, especially when particles are less than 100 μm in size.

We propose an all-dry coating process that allows particles below 100 μm in size and down to the nanoscale to be conformally coated with polymers. This process, which we named initiated chemical vapor deposition (iCVD), relies on the thermal decomposition of a free radical initiator in the vapor phase, the adsorption of activated initiator and monomer vapors on a surface, and the subsequent radical polymerization on the surface to form a coherent polymer coating. Unlike plasma enhanced CVD, another CVD variant for polymerization, iCVD is demonstrated to produce exceptionally clean, stoichiometric polymers without the undesirable crosslinking or branching inherent in PECVD.

We have used iCVD as a way to design the surfaces of micro and nanoparticles by introducing specific functionalities into the polymer coating directly or through post-deposition grafting of functional molecules onto the polymer coating. FTIR and XPS data detailed the chemistries involved, demonstrating the stoichiometry of iCVD polymers. SEM, TEM and AFM revealed the conformal nature of these coatings down to the nanoscale, demonstrating the ability to coat without agglomeration and with tunable coating thicknesses in the nm to μm range. In particular, we have used iCVD to develop suitable pH-sensitive coatings for the controlled release of drug microparticles, being able to incorporate a pH-dependent release as well as minimize undesirable burst release during the initial period of drug dissolution.